Of course class still matters – it influences everything that we do

Nobody wants to believe that British society is as class-bound as it is. Tens of millions watched The X Factor in the belief that talent and effort will rule in the end. We like to think that, while schools like Eton exist, in essence, Britain is a 21st-century democracy where merit, rather than privilege, is the route to the top.

So when Gordon Brown joked about David Cameron, Eton and inheritance tax, the media and most of the political class responded with one voice: the crack did not describe reality, demeaned the joker and didn't work. It was another classic Brown misjudgment, a signal that he was adopting a core vote strategy and was out of touch. The cabinet, after the botched attempt at ousting him, has now secured a promise that such temptations are to be firmly resisted in future.

But the extraordinary level of condemnation, inflating the importance of one – quite good – joke in prime minister's questions shows how raw the subject remains. For while most people would like to believe we "have got past" worrying about the role of Eton and private education because it is no longer said to matter, the social truth will out. Britain is a chronically unfair and increasingly closed society and private education plays a central role. Worse, an unfair society cripples the economy. Open, dynamic societies lead to open, dynamic economies.

Humans are keenly aware of a sense of fairness. We formulate intentions, exert ourselves to deliver them and the outcomes are there for all to see. We expect to be proportionally rewarded for our efforts in producing good results and duly punished for bad ones. Of course there is good luck – of family, talent and natural advantages – and bad. By and large, we consider good outcomes delivered by good luck to be less valuable than those delivered by effort and the sweat of our brow. You can't stop people thinking these things; it is as natural as love and fear. It is not envy that inspires discussion of private schools – it is a sense of fairness.

For the distribution of reward and positions in today's Britain does not mainly correspond to proportional talent, effort and virtue. It has been largely predetermined by the good luck of to whom and where you were born. There are 10 million men and women in work earning less than £15,000 a year; nearly all their parents were in the same position, as will be their children. There are nearly 3 million people of working age who do not even make themselves available for work, again reproducing itself through the generations.

Meanwhile, the middle and upper classes are becoming increasingly effective at ensuring that their children have the capabilities and qualifications to populate the upper echelons of the economy and society, what the great sociologist Charles Tilly called opportunity hoarding.

The good luck of being born into the right family is profound. Two American researchers, Betty Hart and Todd Risley, show how children from professional families hear on average 2,153 words per hour compared with 616 words per hour for kids in welfare families, so that by the age of three, there is a 30 million word gap between the vocabularies of children of families on welfare and those of professional families. On top, welfare children hear words of discouragement twice as often as they hear words of encouragement; children of professional families are encouraged more than 10 times more than they are discouraged. Don't get born into a family on welfare in a council house.

This flows straight through to children's cognitive development – brains are at their most plastic in the early years of development. Data from the <a href="http://www.esds.ac.uk/longitudinal/access/ncds/l33004.asp" title="National Child Development SNational Child Development Study show that there is a strong relationship between children's performance in maths and readings tests and their parents' earnings – a proxy for their class. A boy whose father earns twice another's will score 5% more in maths.

Which is why the now near-universal view that there is a deserving and undeserving poor is so unfair. The dice are loaded against the child born into a disadvantaged family. It is the language used in the home, diet, the capacity to borrow, clothes, housing, quality of schools and the availability of work, especially outside Britain's gilded regions. You can work like a Trojan to get out of these traps, but still be stuck. And the old corrective institutions – trade unions, co-operatives, factories – are much feebler. The gleeful condemnation of the poor as sponging chavs and the delight with which Little Britain's brilliant creation Vicky Pollard is seen as accurately representing today's poor – deserving of being there – masks the brute reality. This is bad luck superimposed upon bad luck, which Britain has been singularly poor at redressing.

By contrast, the rich believe they deserve their status. They're not lucky; they've worked hard and owe nothing to any public institution or society. Wealth is seen as a sign of worth in itself and to be so deserved that if menaced with taxation you threaten to leave the country. Philanthropic giving is actually down.

Society likes wealth. The objection is if it is disproportional to effort, socially useless, has been largely brought about by luck or if those who have it disclaim any social debt or responsibility. Alan Milburn's lethal report on social mobility showed that, despite only 7% of children being privately educated, 75% of judges, 70% of finance directors, 45% of top civil servants and 32% of MPs were independently schooled. And if current trends continue, tomorrow's professionals will come wholly from the better-off 30% of families.

Yet the media have a tin ear on this. Few leading lights in the media send their kids to state schools. Opening up this argument is unwelcome. Private schools are seen as an entitlement of choice and a response to an instinct that rivals fairness – doing the best for your child. They confer advantage in the same way that a professional family's vocabulary confers advantage. What are we meant to do? Stop being middle class?

No one is arguing for stopping being middle class or wanting to do the best for one's children. But our children will want to be part of a resilient, dynamic society that in turn generates a dynamic economy with lots of opportunity. They will also want to know that what they did in life they did fairly, and not to have to produce an excuse for their unfair start, with all its psychological and political consequences. We owe it to them to create social structures that deliver that, not structures that manufacture good luck for those who can pay for it and close down opportunity and openness for everyone else. A few do well, but in a poorer society and economy.

David Cameron can claim to have made the most of his luck, a luck he acknowledges. However, the fact remains that he had the luck for which Britain does too little to compensate. Those who weren't so lucky know how unfair it is; they feel it instinctively. Certainly, Labour and the prime minister should stop harping on about Eton and toffs; it cheapens the whole debate. But they should talk their heads off about fairness, including private education. The media effort to close the conversation down as irrelevant should be resisted. Only those without the advantage have the right to say that private education no longer matters. And they never will.

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